Grid structure for cathode-ray tubes designed for polychrome image reproduction



MW, 27, 1956 L. J. COOK ET9L 2,772,376

GRID STRUCTURE FOR CATHODE-RA TUBES DESIGNED FOR POLYCHROME IMAGE REPRDBUCTION Filed. Jan. 14, 1954 2 Sheets-Sheet l BY Lawrence 7. Quay/1aUnited States Patent GRID STRUCTURE FOR CATHODE-RAY' TUBES DESIGNED FORPOLYCHROME IMAGE REPRO- DUCTION Application January 14, 1954, Serial No.404,038

11 Claims. (Cl. 313-78) The present invention relates to cathode-raytubes of the type adapted to effect the reconstitution of polychromeimages. More particularly, the invention relates to a grid structure forsuch cathode-ray tubes which is characterized by its adaptability tomass production techniques and also by its simplicity of design.

Cathode-ray tubes having a grid of essentialy parallel wires locatedadjacent to a striped phosphor screen are now known in the art. Such atube structure may in some cases serve to focus the beam electrons intoa pattern of thin lines nominally registered with discrete phosphorareas of the screen, as heretofore disclosed by Ernest 0. Lawrence as,for instance by his copending United States patent application SerialNo. 234,190 filed June 29, 1951 and his United States Patent No.2,692,532, granted October 26, 1954.

One type of cathode-ray tube incorporating the above principle (whichmay be termed post-deflection-focusing) is designed with a relativelylarge number of narrow component-color phosphor strips laid down in apredetermined sequence to form a screen, or target electrode. Thesephosphor strips luminesce, when impacted by the cathode-ray beam, invarious component colors of the image to be synthesized. Purely as anexample, the order in which the phosphor strips are laid down may bered, green, blue, red, green, blue, etc., bearing in mind that the colorof a phosphor as used herein refers to the color of the light emittedtherefrom which is seen by an observer. An electrically-conductivecoating overlies the phosphor strips, and is produced in some preferredmanner such as by aluminization.

A grid assembly is located adjacent to the phosphor screen, and, withthe latter, comprises a structure of the type to which the presentinvention is particularly applicable. This grid is formed of a largenumber of wires, or linear conductors, extending in the same directionas the phosphor strips and lying in the path of electrons directed tothe target electrode from the electron gun of the cathode-ray tube. Thewires of the grid assembly are electron-optically related to thephosphor strips so that, in this electron-optical sense, there is a wirealigned with the boundary between each color group, or cell, consistingof at least a portion of a phosphor area representative of each of thecomponent colors. It should be borne in mind that this electron-opticalalignment incorporates whatever corrections are necessary to compensatefor variations in tube operation, such as by changes in theinstantaneous angle of impingement of the cathode-ray beam as it scansthe target. However, the above forms no part of the present invention,and is mentioned merely as an aid in understanding a tube of the natureset forth.

Between the actual or nominal plane of the wire grid assembly and theconductive coating on the phosphor strips a difference of potential isestablished. By properly choosing the magnitude and polarity of thispotential ditference, a series of converging electrostatic fields forthe beam electrons is created. These con- "ice verging fields (which maybe likened in. an optical sense to cylindircal lenses) cause the beamelectrons arriving at the wire grid from the electron gun of the tube toform a fine line structure on the phosphor target. It will beappreciated that the particular scanning operation by means of which thebeam electrons are caused to trace a raster at the plane of the gridwires has no direct geometrical relationship to the actual linestructure developed on the target electrode, the latter being determinedsolely by the configuration of the wires of the grid assembly.

In designing one grid structure of the above type, the wires aremaintained in position relative to the phosphor strips of the target bymeans of spacer elements. The spacing between the plane of the gridwires and the phosphor-coated surface of the target is critical in manyrespects and must remain substantially unchanged during operation of thecathode-ray tube. One preferred construction in which the grid wires andthe phosphor screen are formed as a unit is illustrated and described ina copending United States patent application of Reno Zaphiropoulos,Serial No. 307,435, filed September 2, 1952.

In the Zaphiropoulos assembly, a light-transmissive base plate (whichmay be of glass) is employed as a target backing. This base plate issecured to a grid frame by the strand conductors, or wires, of the grid.A pair of spacer bars is atfixed to one surface of the base plate, anddefines a window, or target area, therebetween which may be coated withphosphor strips having the desired color characteristics. Means areprovided for securing the electrically-conducting wires to the frame sothat these wires extend across the window, or target area, of the baseplate and are positioned therefrom by the spacer bars. Inasmuch as thegrid structure being described is designed for color switching, ormicro-deflection, of the beam in the vicinity of the target electrode,the wires, or linear conductors are divided into two sets of alternatestrands, and suitable means are provided for applying potentials to eachset of strands. To carry this out, the frame is divided into twosections, with each section serving a separate set of strands and alsobeing electrically insulated from the other. Consequently, in this formof construction, the glass plate is sandwiched between the wires of thegrid, on one hand, and the two frame sections on the other. These twoframe portions are pressed together by the tension of the wiresassociated with the outer frame portion, and this pressure acts to holdthe frames, base plate and wires in a unitary assembly.

A structure such as described in the above-mentioned Zaphiropoulospatent application is designed for use with a single-guncolor-reproducing cathode-ray tube in which the grid assembly acts as acontrol means for changing the color of the light emitted from the tubein accordance with particular values of potentials applied to thediiferent parts of the grid. The grid structure of the presentinvention, however, is intended to be utilized in con junction with amultiple-gun cathode-ray tube of the type set forth in above-mentionedLawrence application Serial No. 234,190. Although there are manysimilarities between the two types of structures, nevertheless theprinciple of operation of the one described in the Lawrence applicationcalls for a color-reproducing cycle in which the particular colordisplayed is dependent upon the angle of incidence of the cathode-raybeam at the plane of the grid wires. There is no auxiliary, ormicrodeflection, produced by the grid assembly, and all of the wires ofthe grid are maintained at the same potential relative to that of theconductive coating on the phos' phor screen. As a result of thispotential difference, and with proper spacing between the grid assemblyand the screen, all of the electrons passing between any adjacent pairof wires are brought to a focus area of much smaller width than the wirespacing. Since there is no necessity for dividing the grid intoelectrically-insulated sections, it has, been found possible by means ofthe present invention to simplify to a considerable degree theconstruction of the grid unit over that set forth by Zaphiropoulos,especially in the sense of making itmore applicable to mass production.

Although the color grid structure set forth by Zaphiropoulos in hisabove-mentioned patent application is completely satisfactory. insofaras operation is concerned, and produces an image in which there issubstantially no color contamination, nevertheless it is somewhat time-.consuming to manufacture due to the techniques which must be employed.As presently constructed, each set of grid wires is attached to itsassociated frame section by hooking the wire over a projection on theframe, laying down the wire across the raster area of the base plate,hooking it over a projection on the opposite side of the same frame,bringing it back across the raster area of the base plate, and so on. Awinding operation is thus carired out which, While producing a grid ofsatisfactory operating characteristics, nonetheless requires aconsiderable amount of time to complete and hence materially reduces thenumber of units that may be manufactured within a given time period.

In an attempt to shorten the time required for fabricating such colorgrid structures, an alternative method was devised. This is set forthboth in the above-mentioned application of Renn Zaphiropoulos, SerialNo. 307,435, as well as in his further application Serial No. 307,436filed concurrently therewith. This consists in winding the gridcontinuously around the base plate to eliminate.

the back=and-forth motion previously employed. Inasmuch as this left aset of wires on the rear, or viewing, side of the base plate which hadto be removed prior to operation of the tube, it was necessary to anchorthe wires-near the two extremities of the base plate, and this was doneby cementing them in position so that the portion of each turn of wirewhich was unnecessary to tube operation might be cut out and discarded.While eliminating one objectionable feature of previous methods ofconstruction, this last-mentioned technique added a step of cementingthe wires in position and then a further step of cutting out one portionof the continuously-wound assembly. This used up a considerablepercentage of the time saved by eliminating the back-andforth windingoperation. Furthermore, all the tension of the wires in such aconstruction is exerted through these cementitious bindings, and thereis always a possibility present that'the latter will not be sufiicientlystrong to hold the tensioned wires in position. Nevertheless, thestructure just described was a step in the right direction towarddeveloping a grid assembly which could readily be mass produced.

According to a feature of the present invention, a substantiallyrectangular grid frame is employed around which a continuous conductoris wound in an uninterrupted fashion. This results in two sets or groupsof parallel wires which lie in different planes; However, means arefurther provided for applying pressure to the strand conductors of oneof these sets relative to the other to cause each strand to assume aposition wherein both sets of wires are essentially coplanar. inasmuchas the above design does not comprehend a physical connection betweenthe wire strands and the glass base plate upon which the coloredphosphor strips are deposited,

these two members are brought into juxtaposition so that the coplanarWire strands are indexed in notches in a pair of spacer bars carried bythe glass plate. When the plate (and its support) are secured to thegrid frame, a unitary structure results. All of the operations mentionedabove may be carried out by simple mechanical means, thus permitting arelatively low cost of manufacture.

One object of the present invention, therefore, is to provide animproved type of cathode-ray tube designed for the reconstitution ofpolychrome images.

A further object of the present invention is to provide a gridstructure, for cathode-ray tubes designed especially but not exclusivelyfor polychrome image reproduction, in which the various portions of thegrid may be readily fabricated and then these portions assembled intoannitary tructure.

A still further object of the present invention is to provide a gridstructure for cathode-ray tubes designed especially but not exclusivelyfor polychrome image reproduction in which the strand conductors of thegrid are wound in a continuous uninterrupted fashion.

An additional object of the invention is to provide a method ofmanufacturing a. grid; structure of the above nature.

Other objects and advantages of the present invention willbe apparentfrom the following description and from the drawings, in which:

Figure l is a semi-diagrammatic view of a cathode-ray tube showing incross section a color grid structure-in accordance withthe presentinvention;

Figure 2- .is a plan view of the color grid structure of Fig. l as seenfrom the electron gun end of the cathoderay tube;

Figure 3 is a detailed View of a portion of Fig. 1;

Figure 4' is. a perspective view of Fig. 3, showing in addition onemanner of securing the base plate assembly to the wire grid unit;

Figure 5 is a perspective view of a portion of Fig. 3, showing infurther detail the, manner in which the two sets of grid wires arebrought into substantially coplanar relationship;

Figure..6 is amodification of a. portion ofthe assembly shown in Figs;l, 2, 3, 4 and 5; and

Figure 7' is a plan, viewof a portionofthe target area of Fig. 2,showingone preferred relationship. between the grid wires and phosphorstrips.

Referring nowto the drawing, there is shown in Fig. l a cathode-ray tubecertain parts of which are conventional. For example, in the neck end ofthe tube, and within the envelope 10, there .is an indirectly-heatedcathode 12 which acts'as a source of electrons for develop ment into ascanning beam. The latter is indicated schematically by the trace 14.Adjacent to, and partially surrounding, the cathode 12 is-a control grid#1, or electrode, 16 suitably apertured to permit the passage ofelectrons which are subsequently formed into the beam 1d. The controlgrid 16, functions in the usual manner to'modulate the emitted stream ofelectrons in accordance with the potential applied thereto relative tothe cathode 12. Also in the neck of the tube there is provided a firstanode or grid #2 (identified by the reference numeral 18) to whichsuitable potentials may be applied so as to result in an .initialacceleration of the electrons emitted from the cathode 12. Adjacent togrid- #2 there is positioned a. second anode or grid #3 (referencenumeral 20) for supplying an additional acceleration to the'electrons.

Defiecting coils, comprising a horizontal pair 22 and a vertical pair24, are provided for the usual scanning purposes. Obviously, the termshorizontal and vertical are used herein in a descriptive sense only.Thus, the electron beam 14 is caused to scan a phosphor-coated target,or light-transmissive base plate 26, to produce light which isvisi'blethrough the end wall 28 of the envelope 10.-

Shown in Fig. 2 is a substantially rectangular support, or frame, 30adapted to fit within the envelope of the cathode-ray tube. This frame30 is made up of'a pair of oppositely-disposed L-shaped channel members32, which form two sides of the frame, and a pair of grooved sidemembers 34, which form the remainingtwo sides. The L-shaped members 32are respectivelysecuredfto the side members 34 by rivets 36 one of whichis shown in each of Fig. 4 and 5. Each side member 34 is of generallyflat configuration, and may be fabricated, for example, from 0.062 thicktype 430 stainless steel sheet bent double as indicated in the drawing.However, the particular manner of fabricating the frame 30 forms no partof the present invention, and any indication that it may be formed bybending and riveting operations is merely for the purpose ofexplanation.

The frame 36 is provided at each corner with a lug or tab 38 which isshown in Fig. 2 as having a contour generally similar to the internalperiphery of the envelope 10. In the case of a metal envelope 10, smallangles 40 may be welded to the inside surface of the envelope atpositions where it is desired to attach the lugs 38. The lugs are joinedto the angles by means of bolts or rivets 42 which preferably passthrough ceramic bushings (not shown) which are provided with insulatingdiscs on each end to isolate electrically the frame 30 from the envelope10. Other means of attachment may be employed, especially when glassinstead of metal envelopes are used. However, since these constructionalfeatures form no part of the present invention, and furthermore arementioned in the above-referred-to Zaphiropoulos applications, nofurther details in regard thereto will be set forth herein.

A continuous filamentary conductor (such as #302 stainless steel of 6mil. thickness) is wound around the oppositely-disposed frame sidemembers 34 in coil-like fashion so as to form two sets of strands. Onesuch set of strands (indicated in the drawing by the reference numeral44) is composed of those which pass over the upper surface of eachgrooved side member 34 (as best shown in Fig. and the other set ofstrands (identified as 46) is composed of thosepassing above the undersurface of the side member. It will be apparent from a consideration ofthe drawing, and especially from Figs. 3, 4 and 5, that these two setsof strand conductors would normally lie in separate planes one above theother, the distance between the planes being determined by the thicknessof the grooved side member 34.

As has been previously brought out, it is highly desirable that all ofthe strand conductors of the wire grid assembly be essentially coplanar,so that the beam electrons passing between the strands can be properlyfocused upon desired areas of the base plate 26. In order to establishsuch a coplanar relationship of the wires, those strand conductors whichconstitute one set (such as 44) are compressed, or forced into aposition in which they are not only coplanar with the other set ofconducting strands but also so that they are interleaved with thelatter. Thus, the wires of one set alternate ,with the wires of theother.

The manner of bringing this about is illustrated especially in Figs. 3,4, and 5, and comprises in part a wire-aligning bar 48 which is securedto and carried by the two oppositely-disposed L-shaped channel members32 of the frame 39. This wire-aligning bar 48 may be composed of thesame material as the frame 3t), and is so designed that, when it issecured to each of the channel members 32 by an angle 50 (Fig. 5)riveted both to the wire-aligning bar 48 and to each frame member 32,the lower edge of the wire-aligning bar is substantially coextensivewith the strand conductors 46 (note especially Fig. 3). In other words,when this wire-aligning bar 48 is properly positioned following theformation of the two sets of conducting strands, such a positioningoperation forces the upper set of strands (44) into coplanarrelationship with the lower set of strands (46). When the bar 48 isriveted to the members 32 through the angles 50, this coplanarrelationship of all of the strand conductors will normally be maintainedthroughout the life of the cathode-ray tube of which the grid assemblyforms a part.

In order that the strand conductors shall be substantially equallyspaced apart (as best shown in Fig. 5) when the wire-aligning bar 48 isin position, it is necessary that the wires of one set be ofiset withrespect to the conductors of the other set, so that application of pressure to one such group will cause the individual wires of the groups tobe interleaved with respect to one another when the coplanarrelationship of all of the conductors is established. One method ofaccomplishing this is by forming a series of grooves 52 in the outeredge of each of the side members 34. Obviously, if these grooves 52 areso aligned to be perpendicular, or normal, to the respective planes ofthe strand conductors 44 and 46 which extend between the members 34 andacross the window area of the frame 30, then the corresponding wires ofthe two sets of conductors would be positioned one above the other, andpressure upon one set (when the wirealigning bar 48 is place inposition) would cause a physical contact between the two sets ofconductors which would not be satisfactory for the purpose of thepresent invention. Consequently, the strand conductors of the two groups44 and 46 are caused to be offset by means of a properly chosendirectional alignment of the grooves cut into the side members 34. Thisalignment is so selected that, when a particular arriving wire strand islooped around the outer edge of one of the side members 34, this loopingoperation results in the returning strand lying midway between twoadjacent wires of the upper set, considered in a direction normal to theplane of the wires. Expressed differently, these grooves are cut intothe outer edge of each of the side members 34 in a predetermineddirection which is other than normal to the plane of the grid wires. Theparticular angle at which the grooves 52 are cut will depend at least inpart upon the thickness of the frame member 34, but in any event will beso chosen that the returning wires, following their looping around theedge of the member 34, will respectively lie midway between theapproaching wires of the grid. Consequently, a grid structure ofcoplanar wires is formed in which all of these coplanar wires aresubstantially evenly spaced from one another, and in which all of thewires are maintained under a selected degree of tension determined bythe winding operation. The backing area, or base plate, 26 carries onone of its surfaces a series of phosphor strips laid down in a mannersuch as will be described in connection with Fig. 7. That is, thesequence of these phosphor strips may be, for example, red, green, blue,red, green, blue, and so on. For proper operation of the tube beingdescribed, it is desirable that each of the strand conductors (whichhave been brought into coplanar relationship in the manner previouslyset forth) be electron-optically aligned with the junction betweenadjacent groups of color strips. To bring this about, a pair ofinsulating spacer elements or bars 54 are securely aflixed to onesurface of the base plate 26 in the manner best shown in Figs. 2, 3 and4. These spacing bars, as well as the translucent base plate 26, maycomprise bore-silicate glass, but in any event should have the samecoefficient of expansion. These spacer bars perform the dual function ofaligning the coplanar wire strands with the phosphor strips and alsomaintaining the wire strands at a uniform distance from the surface ofthe base plate 26.

The base plate 26, with its pair of spacer bars 54, is mounted in a pairof L-shaped support members 56, one of which is shown in Figs. 3 and 4.The plate 26 is cradled in each L-shaped member 56 in the manner shown,the latter members being preferably composed of the same material as theframe sections 32 and 34.

There have now been described two units, or subassemblies, one of whichmay be designated as the grid wire sub-assembly, as shown in Fig. 5, forexample, and the remaining one constituting the base plate sub-assembly,which includes the phosphor-coated glass plate 26, the spacer bars 54secured to one surface of this plate,

and the support members 56. These two sub-assem bliesare nowbroughttogether so. that the coplanar wire conductors of the unit shownin Fig. 5. respectively fall within grooves in the upper surface of thespacer bars 54. In other words, these two units are brought into theposition best shown in Figs; 3 and 4, with the upperedge of the spacerbars 54 contacting the coplanar wires-of the assembly of Fig. 5 withjust enough pressure'to maintain the conductors of the grid wireassembly properly indexed within the grooves or notches cut into theupper surface of the spacer bars 54. In this position, the two units aresecured together by means such asthe angles 58, one of which is shown inFig. 4. The rivet 36 which secures together one of the L-shaped channelmembers32' and one of the grooved side members may also pass throughthis angle 58 as best shown in Fig.4, while another rivet 60 securesthis angle 58 to the L-shaped support member 56. Obviously, four suchsecuring means are employed, one on each corner of the frame 30.

While there has been described above an embodiment of the inventionwherein the side members 34 of the frame 30 are provided .with a seriesof grooves into which the individual wire strands are respectivelyreceivable, nevertheless it may be desirable to index the wires inposition by means of V-shaped notches 62 formed in the aligning bar 48,as shown in Fig. 6. These notches 62, equal in number to the strandconductors 4.4, are preferably wideenough atthe base to allow for somemisalignment of the wires following the winding operation. When the bar48 is brought into contact with the conductors 44, therefore, each ofthe wire strands will be seated at the apex of its respective notch. Ifnow the bar 48 is given a lateral displacement equal to one-half thedistance between the center of the wires 46, then securing of the bar 48to the frame members 32 by means of the angles 50 will cause each wire44 to lie midway between adjacent conductors 46, and the desiredequallyspaced coplanar relationship is brought about. Obvious- 1y, undersuch conditions, there is normally no need for grooving the side members34.

The relative position of the conducting strands, or grid wires, and thered, green and blue phosphor strips which are applied to that surface ofthe base plate 26 impacted by the electron scanning beam, is shown inFig. 7. Although the particular arrangement of the phosphorstrips formsno part of the present invention, nevertheless a desirablearrangementhas been shown to consist of repeating groups of red, greenand blue strips. The; strip widths are chosen in accordance with tubedesign so as toprovide electro-optical rather than physicalrelationships between the grid wires and the phosphor strips. Eachadjacent pair of grid wires accordingly is designed to subtend (in anelectro-optical sense) a portion of the target electrode surface whichincludes phosphor areas of each of the component colors. General- 1yspeaking, however, it may be said that the distance between adjacentgrid wires is substantially resolved by the cathode-ray tube.

Having thus described the invention, what is claimed is:

1. In a grid structure designed for incorporation into a cathode-raytube adapted to reconstitute images in a plurality of colors, thecombination of a frame having a window area, a continuous conductorwound in coillike fashion around said frame so as to form across saidwindow area two sets of substantially parallel strands respectivelylying in separate parallel planes and a bar of rigid material positionedsubstantially adjacent to the conductor support frame to compress one ofthe sets of parallel strands into coplanar relationship with the other.

2. In a grid structure designed for incorporation into a cathode-raytube adapted to reconstitute images in a plurality'of colors, thecombination of a frame having a window area, a continuous conductorwound in coillike fashion around opposed edges of said frame so as toform-across said window area two sets of'substantially parallel strandsrespectively lying in separate parallel lanes and pressure bar meanssupported from the frame and located substantially adjacent to theconductor support for bringing one of the said sets so that all of thecoplanar strands are substantially equally spaced apart.

3. The combination of claim 2, in which said lastmentioned meanscomprises a notched bar of rigid material, the individual strands ofeach set being respectively receivable in such notches.

4. In a grid structure designed for incorporation into a cathode-raytube adapted to reconstitute images in a plurality of colors, thecombination of two pairs of oppositely-disposed frame members togetherdefining a substantially rectangular Window area therebetween, eachmember of one of said pairs being provided with a series of parallelgrooves on its outer edge, a continuous conductor wound in coil-likefashion around the frame members of said one pair so that successiveturns of said coil lie within adjacent grooves in each such frame memberto form across said window area two sets of substantially parallelstrands respectively lying in separate parallel planes and means forbringing one of the said sets of parallel strands into coplanarrelationship with the other of said sets.

5. The combination of claim 4, in which the parallel grooves on theouter edge of each of the two oppositelydisposed frame members arealigned in a direction other than perpendicular to the plane of each ofthe said sets of strand conductors.

6. The combination of claim 4, in which the parallel grooves on theouter edge of each of the two oppositelydisposed frame members are soaligned that the strand conductors of one group are offset from thestrand conductors of the other group.

7. A grid structure comprising a frame having a window area, acontinuous conductor wound around said frame in coil-like fashion so asto form across said window area two groups of strand conductors lying inseparate parallel planes, means for causing the strand conductors of onegroup to be offset with respect to the strand conductors of the othergroup, means for applying pressure on the conductors in a directionsubstantially normal thereto, as well as normal to the conductor lengthfor bringing all of the said strand conductors into a common plane whichall of the coplanar conductors are substantially equally spaced apartand means for anchoring the conductor displacing means in a positionpermanently to maintain the coplanar conductor arrangement.

8. A grid structure according to claim 7, further comprising atransparent base secured to saidframe,

and so as to lie substantially equidistant from the said coplanarconductors.

9. The combination of claim 8, comprising, in addition, a plurality ofphosphor strips coated upon the base plate in nominal registry with thecoplanar strand conductors.

10. A grid structure comprising a frame having a window area, acontinuous conductor wound around said frame in coil-like fashion so asto form across said window area two groups of strand conductors lying inplanes which are separate yet parallel to one another, means for causingthe strand conductors of one group to be offset with respect to thestrand conductors of the other group, means for bringing all of the saidstrand conductors into a coplanar relationship in which all of thecoplanar conductors are substantially equidistant from one another, atransparent base plate, a pair of spacer bars carried by said baseplate, and means for securing said base plate to said frame so'that saidspacer bars act to contact said strand conductors and thereby maintainsaid strand conductors substantially evenly spaced from said base plateacross that portion of the said window area lying between said spacerbars.

conductors.

References Cited in the file of this patent UNITED STATES PATENTSPidgeon Aug. 1, 1933 10 Clark May 7, 1935 Baker Jan. 7, 1936 Eitel Oct.2, 1945 Boorland Sept. 16, 1952 Lawrence Sept. 22, 1953 Gehrke June 1,1954

